Method for purifying synthetic organic detergents



2,863,837 Fatented Dec. 9, 1958 METHGD FOR PURHFYING SYNTHETIC ORGANIC DETERGENTS Paul Becker, Murray Hill, N. 5., assignor to Colgate- Palmolive Company, New York, N. Y., a corporation of Delaware No Drawing. Application March 26, 1957 erial No. 648,493

12 Claims. (Cl. 260-400) This invention relates to a process for purifying synthetic organic detergents. More particularly, this invention is concerned with removing impurities such as inorganic salts from alkali metal salts of sulfated partial esters of polyhydric alcohols, such as glycerol, with long chain fatty acids having from about 8 to 24 carbon atoms per molecule, and preferably from about 12 to 18 carbon atoms per molecule.

Synthetic organic detergent compounds such as alkali metal salts of sulfated partial glyceryl esters of long chain fatty acids having from 8 to 24 carbon atoms have long since established themselves as standard items of commerce. A very Well-known example of this class of compounds is the mixture comprising the sodium salts of the sulfated partial esters of glycerol with the fatty acids derived from coconut oil and having an average of about 12 carbon atoms per molecule, and for brevity and convenience this compound (or rather, mixture of compounds) will be referred to frequently hereinafter as the prototype of the compounds to which the present invention primarily relates, but without intending any limitation upon the invention by such ellipsis. The partial esters referred to herein are mixtures of the polyhydric alcohol mono-esters and di-esters, with the former generally predominating.

During the course of manufacture of compounds of this type, it is conventional practice first to manufacture partial esters having the desired configuration such as by an alcoholysis-type reaction after which the partial esters are treated with a suitable sulfating reagent such as oleum, etc., whereupon the desired salt-form of the detergent compound is then produced by treating the resulting reaction mixture with a suitable alkali such as sodium hydroxide, carbonate, or bicarbonate. Since the sulfating step is invariably carried out with the aid of excess sulfating agent to insure complete sulfation, the alkali is also employed in excess in order to insure complete neutralization of excess sulfating agent (including the H 50 of the oleum) and therefore the desired sulfated partial ester alkali metal salt product is finally obtained in admixture with an alkali metal sulfate such as sodium sulfate.

For many uses, for example, in the case of dental detergents, shampoos, and the like, it is desirable if indeed not essential to obtain the sulfated partial ester organic salt products in a high degree of purity, and especially free or substantially free from inorganic salts such as sodium sulfate, or other alkali metal sulfate. The separation or isolation of the active ingredient (i. e., the alkali metal salts of the sulfated partial esters) of the organic detergent composition from the inorganic salts or other impurities that may be present may be carried out in a number of Ways, but a particularly desirable way is by solvent extraction by means of a lower aliphatic monohydric alcohol, such as ethanol or isopropanol. lsopropanol is especially desirable, particularly when the synthetic detergent compound is intended for use as a dental detergent.

The process of this invention is eminently suited tothe treatment of synthetic organic detergents of the sulfated type. Particularly desirable results are obtained in the treatment of lower aliphatic monohydric alcohol extracts of sodium salts of sulfated partial glyceryl esters of long chain fatty acids having from 8 to 24 carbon atoms per molecule, and preferably from 12 to 18 carbon atoms per molecule. Specific examples of these are sodium salts of sulfated glyceryl partial esters, and especially sulfated glyceryl mono-esters of coco-fatty acids, tallow fatty acids, mixed coco-tallow fatty acids, hydrogenated coco-fatty acids, hydrogenated tallow-fatty acids, hydrogenated coco-tallow-fatty acids, etc. While the process is described more particularly in reference to the synthetic organic detergent compounds in the form of their sodium salts, the process is also applicable to other corresponding alkali metal salts such as potassium salts as well as the ammonium salts.

The alcohol extraction step may be carried out batchwise or in a continuous manner according to procedures per se well known in the art. The net result of such an extraction operation is to effect a separation of the alcohol-insoluble components, including the bulk of the inorganic salts such as sodium sulfate, on the one hand, from the alcohol-soluble components, including the sodium salts of the sulfated partial esters on the other hand. The active ingredient of the composition (i. e., the sodium salts of the sulfated partial esters) is thus obtained in the form of an upper extract layer having a relatively low inorganic salts content, say 5% more or less.

However, this extract layer from the alcohol extraction step still contains the desired active ingredient in admixture with a portion of the inorganic salts, and for many purposes it becomes necessary thereafter still more completely to remove the inorganic salts from the active ingredient, especially when the synthetic organic detergent compound is intended for use as a dental detergent or the like.

Accordingly, this invention relates to a method for removing at least a substantial portion of the inorganic sulfates found in the alcohol extract. It has.been discovered that the addition of a quantity of magnesium sulfate to the alcohol extract results in the formation of two layers. The upper layer comprises the synthetic organic detergent in alcohol, while the lower layer is a saturated solution comprising a substantial portion of the inorganic sulfate and magnesium sulfate. Any solid magnesium sulfate and inorganic sulfate that separate from the saturated solution do so as the double salt astrakanite. While the use of magnesium sulfate represents the preferred embodiment of this invention, other compounds that form double salts with the inorganic sulfate may be satisfactorily employed. Another com pound useful in the practice of this invention is potas sium chloride. Mixtures of magnesium sulfate and potassium chloride may also be employed. For brevity and convenience magnesium sulfate will frequently be referred to hereinafter as the prototype of the compounds to which the present invention primarily relates, but without intending any limitation upon the invention by such ellipsis.

Generally, it is an object of the present invention to provide a process for purifying synthetic organic detergents by removing inorganic salts therefrom.

it is an additional object of the present invention to provide a process for decreasing the amount of inorganic salt associated with an organic synthetic detergent.

It is still another object of the present invention to provide a synthetic organic detergent of the sulfate type that is substantially free of inorganic salts associated therewith.

It is yet another object of the present invention to provide an easily concentratable synthetic organic detergent of the sulfate type in a lower alcohol solution.

Additional objects and advantages of the present invention will become apparent from a detailed consideration of the following description.

To accomplish the above-mentioned objects, this invention contemplates, in general, the addition of a quantity of magnesium sulfate to a mixture comprising alcohol, neutralized sulfated partial esters of the type described above, and inorganic sulfate. For purposes of convenience, the neutralized sulfated partial esters may be referred to as detergents. The detergents are produced by sulfating the partial esters with oleum, or other sulfating agent, which is followed by neutralization with some suitable material, such as sodium hydroxide, giving the neutralized partial esters and inorganic sulfate. The detergents are extracted from the resulting reaction mixture with alcohol. Unfortunately, some of the inorganic sulfate is unavoidably extracted with the detergent. To remove all or substantially all of this residual inorganic sulfate the magnesium sulfate is added to the extract, preferably with agitation and while heating such as to approximately 110 F. After the magnesium sulfate has dissolved, the mixture is permitted to settle resulting in two layers. The upper layer comprises the detergent and alcohol, while the lower layer contains water and a substantial portion of the remaining inorganic sulfate, apparently in the form of double salt of the alkali metal sulfate with magnesium sulfate.

The solids content (including content of the active detergent ingredient) in the detergent-alcohol layer is in this way increased considerably. In order still further to increase the solids content the mixture may now be subjected to ordinary fiash evaporation without the formation of gels which often occurs when one attempts to increase the solids content by an ordinary evaporative concentration step applied to the detergent and alcohol mixture without first having treated same with magnesium sulfate in accordance with the present invention.

More particularly, this invention contemplates the addition of between about 5 and parts of magnesium sulfate per hundred parts by weight of the detergent-alcohol extract having between about and solids con tent. The amount of magnesium sulfate added depends upon the amount of inorganic sulfate present. It is not desirable to add substantially more magnesium sulfate than is necessary to take up substantially all of the inorganic sulfate as a double salt. nesium sulfate in excess of this will react with the detergent to form a substitution product and thus decrease the total yield of active detergent ingredient.

In each of the subsequent examples, the quantity of magnesium sulfate is varied. Parts are by weight unless otherwise indicated or required by the context. However, the quantity of magnesium sulfate may be further varied from those set forth; therefore, the following examples are illustrative of the invention but are not to be construed as placing limitations on the scope other than as set forth in the appended claims.

Example I A partial ester of glycerol and the fatty acids derived from coconut oil is sulfated with oleum in the usual manner. To this mixture a sufficient amount of sodium hydroxide is added to neutralize the sulfated partial esters and the excess sulfating reagent. The resultant is a mixture of neutralized detergent base and sodium sulfate. To approximately 150 parts of the resultant, parts of isopropanol are added accompanied by agitation until fully mixed. The mixture is permitted to settle. Two layers form. The lower layer contains most of the inorganic sodium sulfate. The upper layer is decanted; and contains the following parts per hundred An amount of magby weight: 22.96 parts of isopropanol, 37.38 parts of water and 39.18 parts of solids. Additionally, 94.08% of the solids are alcohol solubles. parts of this decanted upper layer are treated with 15.0 parts of anhydrous MgSO In order to dissolve the MgSO the mixture is agitated and heated to F. When the MgSO is dissolved the mixture is permitted to settle into two layers. The lower layer contains nearly all of the MgsO some of the inorganic sulfate, water and a small quantity of alcohol. The neutralized detergent base in the upper layer is substantially richer in active ingredient. The upper layer contains 28.49 parts per hundred by weight of isopropanol, 25.86 parts of water and 45.65

parts of solids. The alcohol solubles content of the solids has increased from 94.08% to 97.46%.

Example 11 An isopropanol solvent neutralized detergent upper layer is produced as in Example I. The upper layer has a 39.18% solids content which is 94.08% alcohol soluble. 100 parts of this upper layer are treated with 5 parts of anhydrous MgSO as in Example I and two layers are again produced. The resultant upper layer has a 40.25% solids content which is 95.62% alcohol soluble.

Example III To 100 parts of the initial upper layer isopropanol extract of Example ll, 15 parts of anhydrous MgSO, are added. There is obtained in this way an upper layer having 46.48% solids which are 97.67% alcohol soluble.

Example IV This example employs 100 parts of the identical batch of initial upper layer isopropanol extract as Examples II and Ill. 15 parts of anhydrous MgSO as in Example III are also employed except that a two-step process is employed. In the first step only 7.5 parts of the anhydrous MgSO are utilized for treating the initial isopropanol extract. The upper layer resulting from this treatment is decanted and then treated with the remaining 7.5 parts of anhydrous MgSO The final alcohol solubles content of the product obtained in this manner comprises 98.11% whereas when employing the one step process as in Example III the alcohol solubles content comprises only 97.67%.

While in this example a two-stage operation is set forth, the efiiciency may be even further increased by utilizing more than two stages. It is entirely possible to employ 5 steps using about 3 parts of anhydrous magnesium sulfate each time. However, the improvement in the product obtained from using a two or more stage process must be balanced against the lesser cost of simply using additional magnesium sulfate in the one-step process.

It is seen that in the preceding examples the magnesium sulfate employed is in the anhydrous form. The invention is not deemed to be limited by this form; rather the heptahydrate form, commonly referred to as Epsom salts, may be utilized. However, the water of hydration must be compensated for by the use of a proportionately larger amount of Epsom salts so that the total amount of magnesium sulfate available will be approximately the same. Approximately twice the "weight of Epsom salts is substantially equal in effect to that obtained by using anhydrous magnesium sulfate. Due to the economies that may be effected, Epsom salts may be preferred. Furthermore, it is entirely within the scope of this invention to employ solutions of magnesium sulfate. However, the use of solutions creates the usual problems incident to diluting the mixture so that the entire operation becomes more costly since proportionately larger quantities of materials will have to be handled.

While the preceding examples disclose a batclnwise operation, the invention is eminently suited for continuous operation. In a continuous operation the magnesium sulfate, either in the anhydrous or heptahydrate form, or in solution, is added to a process stream of detergentinorganic sulfate-alcohol extract. The stream is heated and is agitated by suitable means to dissolve the magnesium sulfate. The separation of the detergent-alcohol phase from the magnesium sulfate-inorganic sulfate double salt is effected in a suitable continuous centrifuge. The detergent-alcohol mixture may then be flowed to a suitable continuous flash evaporator such as for conversion to a dry powder that is substantially inorganic salt free.

The magnesium sulfate when added as a dry powder is dusted into the alcohol extract and stirred until dissolved. In order to effect a relatively quick dissolution the examples recite the application of heat to the mixture. A temperature of the order of approximately 110 F. has been discovered to produce excellent results. However, higher or lower temperatures may be employed successfully. It is to be understood that lower temperatures of operation will require longer periods of agitation before the magnesium sulfate is completely dissolved, while somewhat higher temperatures will, of course, increase the speed with which the magnesium sulfate is dissolved.

The duration of stirring time will also vary with the amount of magnesium sulfate used and with the efficiency of the stirring.

While the broad idea of adding MgSO to a synthetic organic detergent composition of the type herein involved has been suggested heretofore (Bell et al. U. S. Patent No. 2,187,144) it will be noted that the organic sulfates of Bell et al. having a particular cation (e. g., Na) were merely converted to the corresponding sulfates having a I different cation (e. g., Mg).

It will be apparent that many changes and modifications of the several features of the process described herein may be made without departing from the spirit and scope of the invention. It is, therefore, to be understood that the foregoing description is by way of illustration of the invention rather than limitation upon the invention.

What is claimed is:

1. In the method of preparing synthetic organic detergents wherein sulfated partial esters of glycerol and relatively high molecular weight fatty acids and excess sulfating reagent are neutralized with an inorganic salt-forming reagent resulting in a synthetic organic detergent and an inorganic sulfate, and extracting the detergent with alcohol resulting in a mixture comprising detergent, alcohol and undesirable inorganic sulfate, the improvement comprising adding a quantity of a substance capable of forming a double salt with the inorganic sulfate and selected from the group consisting of magnesium sulfate and potassium chloride and mixtures thereof, and thereafter separating a substantial portion of the inorganic sulfate together with the added substance from the synthetic organic detergent-alcohol mixture.

2. The method of claim 1 wherein the substance capable of forming a double salt is magnesium sulfate.

3. The method of claim 1 wherein the substance capable of forming a double salt is added in an amount between about 5 parts to 20 parts per hundred by weight of detergent, alcoholand inorganic sulfate mixture.

4. The method of claim 1 wherein the substance capable of forming a double salt is added in an amount of approximately 5 parts per hundred by weight of detergent, alcohol and inorganic sulfate mixture.

5. The method of claim 1 wherein the substance capable of forming a double salt is added in an amount of approximately 15 parts per hundred by weight of detergent, alcohol and inorganic sulfate mixture.

6. In the method of preparing synthetic organicdetergents wherein sulfated partial esters of glycerol and relatively high molecular weight fatty acids and excess sulfating reagent are neutralized with an inorganic saltforming reagent resulting in a synthetic organic detergent and an inorganic sulfate, and extracting the detergent with alcohol resulting in a mixture comprising detergent, alcohol and undesirable inorganic sulfate, the improvement comprising adding in a first step a quantity of a substance capable of forming a double salt with the inorganic sulfate and selected from the group consistingof magnesium sulfate and potassium chloride and mixtures thereof, thereafter separating a substantial portion of the inorganic sulfate together with the added substance from the synthetic organic detergent-alcohol mixture, and treating the synthetic organic detergent-alcohol mixture in a second step with an additional quantity of a substance capable of forming a double salt with inorganic sulfate and selected from the group consisting of magnesium sulfate and potassium chloride and mixtures thereof, and thereafter separating an additional portion of the inorganic sulfate together with the added substance from the synthetic organic detergent-alcohol mixture.

7. The method of claim 6 wherein the substance capable of forming a double salt is added in the first step in an amount of approximately 7.5 parts per hundred by weight of detergent, alcohol and inorganic sulfate mixture, and the substance capable of forming a double salt is added in a second step in an amount of approximately 7.5 parts per hundred by weight of detergent, alcohol and inorganic sulfate mixture.

8. In the method of preparing synthetic organic detergents wherein sulfated partial esters of glycerol and relatively high molecular weight fatty acids and excess sulfating reagent are neutralized With an inorganic .saltforming reagent resulting in a synthetic organic detergent and an inorganic sulfate, and extracting the detergent with alcohol resulting in a mixture comprising detergent, alcohol and undesirable inorganic sulfate, the improvement comprising adding a quantity of a substance capable of forming a double salt with the inorganic sulfate and selected from the group consisting of magnesium sulfate and potassium chloride and mixtures thereof, heating to about F. and thereafter separating a substantial portion of the inorganic sulfate together with the added substance from the synthetic organic detergentalcohol mixture.

9. The method of claim 8 wherein the substance capable of forming a double salt is magnesium sulfate.

10. The method of claim 8 wherein the substance capable of forming a double salt is added in an amount between about 5 parts to 20 parts per hundred by weight of detergent, alcohol and inorganic sulfate mixture.

11. The method of claim 8 wherein the substance capable of forming a double salt is added in an amount of approximately 5 parts per hundred by weight of detergent, alcohol and inorganic sulfate mixture.

12. The method of claim 8 wherein the substance capable of forming adouble salt is added in an amount of approximately 15 parts per hundred by weight of detergent, alcohol and inorganic sulfate mixture.

No references cited. 

1. IN THE METHOD OF PREPARING SYNTHETIC ORGANIC DETERGENS WHEREIN SULFATED PARTIAL ESTERS OF GLYCEROL AND RELATIVELY HIGH MOLECULAR WEIGHT FATTY ACIDS AND EXCESS SULFATING REAGENT ARE NEUTRALIZED WITH AN INORGANIC SALT-FORMING REAGENT RESULTING IN A SYNTHETIC ORGANIC DETERGENT AND AN INORGANIC SULFATE, AND EXTRACTING THE DETERGENT WITH ALCOHOL RESULTING IN A MIXTURE COMPRISING DETERGENT, ALCOHOL AND UNDESIRABLE INORGANIC SULFATE, THE IMROVEMENT COMPRISING ADDING A QUANTITY OF A SUBSTANCE CAPABLE OF FORMING A DOUBLE SALT WITH THE INORGANIC SULFATE AND SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM SULFATE AND POTASSIUM CHLORIDE AND MIXTURES THEREOF, AND THEREAFTER SEPARATING A SUBSTANTIAL PORTION OF THE INORGANIC SULFATE TOGETHER WITH THE ADDED SUBSTANCE FROM THE SYNTHETIC ORGANIC DETERGENT-ALCOHOL MIXTURE. 